Show notification when user session is expired

### Please agree to the following

- [X] I have searched [existing issues](https://github.com/cryptomator/hub/issues?q=) for duplicates
- [X] I agree to follow this project's [Code of Conduct](https://github.com/cryptomator/hub/blob/develop/.github/CODE_OF_CONDUCT.md)

### Summary

Show notification when user session is expired (and cannot be renewed).

### Motivation

When the accessToken is expired, we automatically refresh the token in
https://github.com/cryptomator/hub/blob/42527eb2dbf76dd5c3186566061e11e97ecdfeb7/frontend/src/common/auth.ts#L13

This might fail, if we reach the Max User Session duration:

Admittedly, in this example, it is very unlikeley to reach this. But that value should be reduced anyway. 😉
After the session end, Hub displays the FetchError component, but retrying would not yield any success. The user needs to reload the page or navigate somewhere to be prompted with the login page.

A notification would be nice, such that the user can save form data elsewhere and react to it.

### Considered Alternatives

_No response_

### Anything else?

_No response_